Tumbler base



FIG. 1 is a perspective view of a tumbler base showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front view thereof; and,

FIG. 4 is a bottom view thereof.

The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a tumbler base, as shown and described. 